The two countries will embark on the first major arms discussions since 1997.
President Obama and Russian President Dmitry Medvedev announced the talks on Wednesday after their first meeting, White House spokesman Robert Gibbs said in London, site of the G20 summit. Both countries want to reduce the number of warheads, but no firm number has been reached.
"We agreed to pursue new and verifiable reductions in our strategic offensive arsenals in a step-by-step process, beginning by replacing the Strategic Arms Reduction Treaty with a new, legally-binding treaty," said a joint U.S.-Russian statement released by the White House after the two men met in London. (Click here to read the full statement.)
"We are instructing our negotiators to start talks immediately on this new treaty and to report on results achieved in working out the new agreement by July."
The leaders agreed to craft a replacement for the expiring 1991 Strategic Arms Reduction Treaty, which limited the world's two largest nuclear arsenals to between 1,700 and 2,200 warheads, known as START, before it expires on Dec. 5.
CBS News White House correspondent Peter Maer reported earlier that, according to an administration source, Wednesday's meeting between Mr. Obama and Medvedev was a scene-setter for a formal U.S.-Russian summit as early as this summer.
During their meeting Wednesday, Mr. Obama accepted an invitation from Medvedev to visit Moscow in July.
The White House official told CBS News that Wednesday's meeting was all about gauging "dynamics" between the two men.
"With the START Treaty expiring in December, the agreement between President Obama and President Medvedev to begin negotiations for a new strategic arms reduction pact ensures that the G20 meeting ends with an accomplishment," says CBS News foreign affairs analyst Pamela Falk, "regardless of the preceived limits of the final communique to come out of the summit."
Mr. Obama's administration has reached out to Russia during its first two months in power, trying to repair a rift that emerged over the United States' plan to build a missile defense system in Eastern Europe that Moscow vehemently opposes. Mr. Obama called a new arms control treaty push "a good place to start" in rebuilding a partnership with Russia.
|Photos: Obama In London|
The president has his first full day in London. (Photo: AP)
Answering questions at a with British Prime Minister Gordon Brown, Mr. Obama lamented tensions and "drift" between Moscow and Washington in recent years. He told reporters that "I have no interest in papering those over," but also said the two countries share many interests, including reducing the threat of terrorism and stabilizing the world economy.
"Both sides of the Atlantic understand that, as much as the constant cloud of nuclear warfare has receded, that the presence of these deadly weapons continues to be the gravest threat to humanity," Mr. Obama said.
Mr. Obama said his country wanted to "press the reset button," a phrase that has been used by other top members of his administration - initially by Vice President Joe Biden - in addressing U.S.-Russian relations.
The Kremlin has made clear it believes it is up to Washington to open the effort with concessions.
U.S.-Russia relations have deteriorated in recent years to their lowest point since the early 1980s.
Mr. Obama has indicated less enthusiasm than predecessor George W. Bush for a proposed U.S. missile defense system based in Eastern Europe, an idea that has enraged Russia.